Hudhaifah bin Al-Yaman (ra) narrated that:
When the Prophet (ﷺ) would sleep, he would put his hand under his head then say: “O Allah, safeguard me from Your Punishment the Day You gather [Your slaves] (Allāhumma qinī `adhābaka yawma tajma`u [`ibādak])” or “you resurrect your slaves (tab`athu `ibādak).”